The invention relates to a device for generating a regulating signal for a direct voltage converter, with the features disclosed in the preamble to claim 1.
Direct voltage converters are used to convert electrical energy between different voltage levels. An exemplary embodiment for a direct voltage converter of this kind is shown in FIG. 1. The input voltage Uin that is present at an input capacitor Cin is converted by means of a step-down transformer into an output voltage U that can be tapped at an output capacitor Cout. This conversion takes place through the use of a series circuit comprised of a power switch S and a choke L, with the cathode of a diode D being connected between the power switch and the choke and the anode of this cathode being connected to a reference potential. The keying ratio of the power switch, which has a field effect transistor, is predetermined by means of a regulating signal R, which is determined through the use of the fed-back output voltage.
This is shown in FIG. 2, which depicts the associated regulating structure. The output voltage U that can be tapped at the output of the regulating segment 1 is fed back to the input side and in a subtracter 2, is subtracted from a voltage reference value that is present at an input E1. A voltage regulator 3 is connected to the output of the subtracter 2 and on the output side, produces the regulating signal. This indicates the keying ratio for the power switch associated with the regulating segment. This keying ratio can be used to adjust or regulate the average voltage present at the choke.
There is another known methodology for producing the above-mentioned regulating signal R by using a current control loop which is preceded by a voltage regulator. This is shown in FIG. 3, which depicts the associated regulating structure. The output voltage U that can be tapped at the output of the regulating segment 1 is fed back to the input side and in a subtracter 2, is subtracted from a voltage reference value that is present at an input E1. A voltage regulator 3 is connected to the output of the subtracter 2 and on the output side, produces a current reference value for a current control loop. A current actual value that corresponds to the choke current is fed back from the regulating segment 1 and is subtracted from the current reference value in a subtracter 4. The output signal of the subtracter 4 is supplied to a current regulator 5 which at its output, produces the regulating signal R for the regulating segment 1.
The device according to the invention for generating a regulating signal for a direct voltage converter, with all of the features disclosed in the preamble to claim 1, has the advantage that it alternatively permits a regulation of the output voltage or a regulation of the current. In addition, operation with output voltage regulation achieves an overload protection by means of limiting the output current.
These advantages are achieved by using a limiter for the current reference value, which is connected between the voltage regulator and the current regulator. This limiter advantageously operates in a variable manner and has an input connection which can be used to supply it with a limit value signal for the current reference value.
Advantageous embodiments and modifications of the invention are disclosed in the dependent claims.